Method and device for producing biogas, which contains methane, from organic substances

ABSTRACT

A three-stage method used for producing biogas having a high methane content from organic substances includes aerobic fermentation, a charring and thermophilic methane fermentation.

BACKGROUND OF THE INVENTION

[0001] The invention entails a method and related mechanism for theproduction of methane rich biogas from organic materials, morespecifically for the production of biogas with a high methane content.In methods of this kind, the organic matter is decomposed by means ofliving micro-organisms and converted to methane.

[0002] Gas, which can serve as an alternative energy source, isgenerated in the decomposition of organic substances. For reasons of itsgeneration, this gas is described as biogas. An important component ofbiogas is methane, which originates from organic or vegetal substancesor their by-products through fermentation or decomposition under closurefrom air. In larger production contexts, it is generated through thegasification of coal or in petrochemical processes and is utilised asheating gas and for combustion power, as well as raw material forsynthetic products, such as (inter alia) acetylene, synthetic gas, HCNand chlorine substitute products.

[0003] Because of methane's importance, it is aimed to achieve a highproportion of methane in the production of biogas. Depending on thelevel of technology, single or double stage fermentation methods areemployed, by which biogas with a methane content of between 40% and 60%is generated from organic material through anaerobic fermentation. Theremaining biogas components in these processes consist to between 25%and 55% of CO², as well as of smaller quantities of nitrogen, hydrogensulphide and other components.

[0004] Hitherto known methods of anaerobic fermentation for thegeneration of methane from organic materials are therefore notcompletely satisfactory with regard to the quality of biogas and thevolumes of methane produced. Particularly undesirable in these processesis the high proportion of approximately 2% sulphur or hydrogen sulphide,because in concentrations from as low as 0.1%, these are troublesome inthe operation of engines and the allied engagement of catalyticconverters.

[0005] In addition, there are further disadvantages related to knownmethods of anaerobic fermentation. Thus, the degree of decomposition isusually around 45% of the dry organic substance and the productionprocesses are relatively unstable, as the micro-organisms involvedtherein are sensitive to environmental changes. A further effect of thisis that any discontinuities of the process, such as occurs duringservicing intervals or repairs and the subsequent resumption ofproduction, means that profitable productivity levels are only attainedsome 12 to 25 weeks thereafter.

[0006] Furthermore, hitherto familiar technologies leave anon-utilisable residue amounting to about 30% to 70% of the inputvolumes, which must be rendered free of harmful deposits. Similarly, theconversion time, i.e. the duration between the input of the organicmaterials to the process and the production of biogas, is relativelylong and takes in the vicinity of between 20 and 30 weeks.

[0007] The known methods are admittedly environmentally neutral withregard to the carbon dioxide economy, however they do not lead to anyreduction in the carbon dioxide burden on the environment. It alsoremains to be considered that the methane from the unmanageddecomposition in nature is 30 times more negatively burdensome for thegreenhouse effect than CO₂.

[0008] U.S. Pat. No. 4,289,625 describes a bio-thermal gasificationmethod whereby organic matter is initially fermented anaerobically andits residue is then carbonised. The gases formed during carbonisationare then converted to methane by means of anaerobic micro-organisms.

[0009] Although the known methods are environmentally neutral in termsof the carbon dioxide economy, they do not lead to a reduction of theenvironment's carbon dioxide burden. Also to be considered in thisregard is the fact that the methane released in the uncontrolled processof decomposition in nature is about 30 times more negatively burdensomethan CO² for the green house effect.

SUMMARY OF THE INVENTION

[0010] The object of the invention is to provide a method and relatedmechanism for the production of methane rich biogas from organicmaterials by means of which living micro-organisms decompose the latterwhile delivering a higher margin of methane and simultaneously avoidingor reducing the negative side effects of this state of technology.

[0011] The foregoing object is achieved by the present invention byproviding a method A method for producing biogas containing methane,comprising: a) contacting organic matter with fermentationmicro-organisms under anaerobic fermentation conditions so as to produceresiduals and gaseous wastes containing carbon dioxide; b) carbonizingthe produced residuals to obtain a charcoal product and wood gas; and c)contacting the wood gas with thermophile fermentation micro-organismsunder anaerobic fermentation conditions to produce biogas containingmethane and mechanisms for carrying out the method.

BRIEF DESCRIPTION OF THE DRAWING

[0012] Preferred configurations and additional developments of theinvention will become evident from the subsequent description withrelated diagrams.

[0013]FIG. 1 is a schematic diagram of the method of the presentinvention.

DETAILED DESCRIPTION

[0014] An inventive method for the production of methane rich biogasfrom organic matter, whereby such organic matter is decomposed andconverted to methane by means of living micro-organisms, thereforeencompasses three methodological steps.

[0015] In an initial methodological step of aerobic fermentation,organic matter is fermented under aerobic conditions by means offermentation micro-organisms. In this process, solid and/or liquidresidues and gaseous wastes containing CO² are formed.

[0016] In a second methodological step of carbonising, residues from theinitial methodological step are burned, such that charcoal orcharcoal-like products and wood gas is formed. The residues from theinitial methodological step, especially the liquid residues, aredehydrated to facilitate the carbonisation process. To this end, commondrying processes are adequate. The water content should preferablyamount to less than 20%. The water liberated in the dehydration processcan be recaptured in the process of biomass flotation.

[0017] In a third methodological step of the thermophile methanefermentation, wood gas from the second methodological step is fermentedunder anaerobic conditions to methane rich biogas by means ofthermophile fermentation micro-organisms.

[0018] Fermentation is generally understood to be the decomposition oforganic matter by suitable micro-organisms such as yeast cells, bacteriaor fungi, particularly moulds. In the initial methodological step ofaerobic fermentation, a chemical conversion occurs, i.e. thedecomposition of the organic material by suitable fermentationmicro-organisms, especially by bacteria. In selecting suitableorganisms, it should be considered that fermentation in a liquidnutrient substrate is preferably characterised by a high level of carbonand hydrogen consumption, a strong increase of the micro-organisms andof their conversion products and/or of a microbially converted substrate(e.g. protein enrichment), as well as of the potential for theproduction of secondary metabolisers (e.g. enzymes, pharmaceuticalagents). Examples of suitable micro-organisms are Aspergillum niger,Pyrococcus furiosus and Escherischia coli.

[0019] In the initial methodological step, nitrogen is reduced andcarbon dioxide is supplemented. The decomposition products essentiallyinclude biocarbons, i.e. a charcoal-like product, as solid residue, aswell as carbon dioxide in the gaseous waste. The biocarbon fermentationproduct contains large quantities of lignin. By controlling thetemperature and the selection of micro-organisms, the fermentation andthe dynamics of the conversion process can be managed. The temperaturewill most advantageously be in the order of between 30° C. and 50° C.,and most preferably between 36° C. and 38° C.

[0020] In the second methodological step of carbonising, residues fromthe initial methodological step are combusted after an optionaldehydration. Carbonising is understood to mean the heating or slowcombustion under controlled air supply reductions or exclusions. In thisprocess, in addition to monomers and dimers, the higher polymers areconverted to wood gas and charcoal products. The charcoals thus producedare an end product and can be utilised as may be considered appropriate.

[0021] The second methodological step is preferably carried out in awood gasifier, in which the cyclonic layering method offers particularadvantages. Compared with a conventional wood gasification system, thismay offer the advantageous feature that—instead of normal atmosphericair—the waste gas from the initial methodological step is recirculated.The application of the CO² rich waste gases from the aerobicfermentation process in carbonising, especially in the carbonisingphase, can be an advantageous feature, because the air volumes formedduring the aerobic fermentation are carbon dioxide enriched and nitrogenstarved, such that they can be reutilised instead of fresh air in theprocess of combustion, especially in the carbonising phase. Because thegaseous wastes from aerobic fermentation are carbon dioxide enriched,the carbonisation process is concomitantly enhanced.

[0022] The wood gas generated in the second methodological step containsa high proportion of carbon monoxide and carbon dioxide, which arereduced to methane in the third stage of the thermophile methanefermentation.

[0023] In the third stage of the thermophile methane fermentation,monomers and dimers, i.e. carbon monoxide and carbon dioxide, aremicrobially reduced to methane. Where required, chemical and/or physicaltreatments can also be executed. The micro-organisms that can beutilised in the thermophile methane fermentation should meet thefollowing conditions: a high consumption of CO² and a strong increase ofmethane-forming micro-organisms. Examples of such micro-organisms areMethonabaktericum Thermoautrophicum, Methanogascina and Methanococcus.

[0024] It may be regarded an additional advantageous feature that otherorganic materials, especially those containing lignin, can be combustedin the carbonisation process along with the solid and/or liquid residuesfrom the aerobic fermentation.

[0025] As yet another beneficial feature, it may be envisaged inthermophile methane fermentation that residues from the aerobicfermentation (after dehydration, if need be) may also be convertedtogether with wood gas from the carbonisation process. In this way, thethermophile methane fermentation can be managed.

[0026] According to another advantageous feature, in which management ofthe thermophile methane fermentation process may also be envisaged, itis suggested that other gases containing carbon monoxide or carbondioxide may also be fermented to methane together with the wood gas fromthe carbonisation process in thermophile methane fermentation.

[0027] As sources of such gases containing carbon monoxide and carbondioxide, the following processes can inter alia be considered:incineration processes, e.g. in heating plants or fossil fuel powerstations; engine exhaust gases; fermenting processes, e.g. in thebrewing industry or yeast manufacturing; carbonisation processes;chemical production runs; natural rotting cycles and industrialprocesses, as well as fuel cells. This form of execution of theinvention thus has the advantage that it is possible to reduce suchwaste materials to energy rich methane while simultaneously reducing theburden on the environment of carbon monoxide and/or carbon dioxide.

[0028] Taking advantage of yet another feature, it is recommended thatthe thermophile methane fermentation be executed by means offermentation micro-organisms that thrive optimally in the range between15° C. and 90° C., preferably between 35° C. and 85° C., but especiallybetween 45° C. and 55° C. or 65° C.

[0029] In terms of this invention, a mechanism for the generation ofmethane rich biogas from organic matter by means of decomposition andconversion through living micro-organisms, in particular for theexecution of the method as per the invention, encompasses an aerobicfermentation reactor for the fermentation of organic matter underaerobic conditions by means of fermentation micro-organisms, in whichsolid and/or liquid residues and gaseous wastes containing CO² areformed, a carbonising facility for the carbonisation of residues fromthe aerobic fermentation reactor, in which a charcoal product and woodgas are formed, as well as a methanogenic fermentation reactor for theexecution of a thermophile methane fermentation, in which wood gas fromthe carbonising facility is fermented to methane rich biogas underaerobic conditions by means of thermophile fermentation micro-organisms.

[0030] A corresponding plant, e.g. for the generation of electricityfrom biomass by means of the method invented, is most advantageouslyconfigured in size according to the quantities of biomass available.Depending upon the biomass availability, plant sizes of (e.g.) 100 kW,200 kW, 500 kW, 1 MW or up to about 8 MW are functional. A plant ofabout 8 MW requires some 100 000 tonnes to 120 000 tonnes of biomass perannum and a space of approximately 10 000 m² to 15 000 m².

[0031] The method invented and the concomitant mechanism have theadvantage that methane gas with a high methane content in excess of 60%or 70% can be produced. It is possible to configure or develop thetechnique in such a manner as to produce biogas with a methane contentof at least 80%, preferably at least 85% and especially at least 90% inreproducible quality.

[0032] The methane is then available as energy carrier or as productionmaterial for chemical syntheses. Thus, for instance, the biogas ormethane can be utilised in smaller power from heat plants, in gas drivensystems or in block heat power stations for the generation ofelectricity and heat, as well as in gas engines.

[0033] An additional advantage of the method invented can be seen inthat it can be executed or controlled in such a manner as to producebiogas with an H₂S content of less than 2%, preferably less than 1% andan especially preferred less than 0.5%. As a rule, a sulphur content ofless than 0.1% or 0.05% should be the objective. By aerobicfermentation, sulphur is oxidised to sulphate, such that the biogas isalmost devoid of sulphur, in contrast to current technology. The methanegenerated is industrially utilisable.

[0034] Furthermore, the degree of decomposition attained by the methodinvented versus the current state of technology is increased and canreach 65% or more, depending on the organic matter introduced. Themicrobial processes also run reproducibly and therefore largely withoutdisruption, because the diverse environmental requirements of themicro-organisms can be specifically controlled and contained by means ofthe invented division of the decomposition of organic matter in aerobicfermentation and anaerobic methanogenesis. The reactivation of aproduction facility in terms of this invention can therefore reach aneconomical performance level within not more than eight days.Furthermore, the method invented functions relatively rapidly, such thatthe processing time for the conversion of an organic material to methanegenerally amounts to only about 16 to 36 hours, during which peakproduction of methane is already attained after approximately 12 hours.

[0035] The end products of the method invented consist of marketablecharcoal as a solid residue and—depending on the raw materialutilised—an end product can even be partially reintroduced into theprocess, i.e. a cascading utilisation of the biomass. Economicallyinteresting by-products also derive from the individual processingstages, e.g. pactins, proteins, vegetal drugs, such as hecogenin acetateor acetylsalicylic acid, which may be extracted accordingly.

[0036] The method invented only leaves mineral components to an extentof between about 3% to 8% of the organic matter introduced as residuals;these raw materials are deposited.

[0037] In additional special forms of. execution, the method can beconfigured in such a way that additional carbon dioxide is reduced tomethane in the thermophile methanogenesis that the CO² burden on theenvironment is reduced.

[0038] With the invention, therefore, objectives are attained, withwhich the world of specialists has long been wrestling. In order to aimfor exceptional results, the heretofore elucidated preferential featuresare introduced below in conjunction with more detailed descriptions atthe hand of a diagram, exemplary, singular or combinations of executionsare illustrated, from which additional beneficial effects may resultthrough the interaction of advantageous features.

[0039]FIG. 1 is a diagram of the method invented, alternatively of arelated mechanism. The organic matter 1, which serves as raw material,can be any organic matter, i.e. a biological organic waste material,e.g. manure, agricultural wastes, clearing mulch, paper mulch, kitchenwaste or other waste biomass in bulk.

[0040] Organic matter 1 utilisable by the method invented include fuels,biomass and energy plants. Fuels may include wastes from sawmills, woodprocessing industries or dead wood clearing, agricultural waste, paper,paper mash and organic sludges. Suitable biomass includes e.g. all typesof organic waste, such as (e.g.) nutrient residues, including residualsfrom food production, husks, feed stock wastes, spoilt groceries,abattoir offal, faeces, production residues from starch manufacture,kitchen wastes, etc.

[0041] Among specific examples can be mentioned: outdated food stuffs,spelt and grain dust, residues from canneries, molasses residues, doughwaste, sludgy wastes, expired confections, tobacco dust, grass, ribs,mulch, cigarette rejects, malt husks, malt sprouts, malt dust, hophusks, fruit, grain and potato peels, drudge and mulches from breweries,grape skins, manufacturing residues from coffee, tea or cocoaprocessing, yeast or yeast-like residues, feed stock wastes, oil seedresidues, fatty wastes (rancid fats), e.g. from slaughter and margarineproduction; content from fat trimmers; flotation residues; dairy, oil,fat or wax emulsions; production residues from creameries. Sludge fromnutrient fat and food oils production; fuller's earth (degreased); bonewaste and skin remnants; entrails; poultry waste; fish wastes; stomach,gut and rumen contents; poultry manure; pig and cattle manure; starchsludge; sludge from gelatine manufacture; gelatine mould trimmings;residues from starch production from potatoes, maize and rice;production residues from food oils manufacture and from cosmeticpreparations; protein wastes; kitchen and canteen waste (from industrialkitchens, etc).

[0042] Possibly utilisable energy plants include (e.g.) China reeds(Miscantus sinensis giganteus), grazing cultures, poplars, sugar canehusks and rapes.

[0043] If required, the organic matter 1 can be prepared in anappropriate pre-production stage 2, e.g. by shredding, drying ordamping, forming, etc. The organic matter prepared thus 3, is thenintroduced into the first invented stage, an aerobic fermentationreactor 4, in which a chemical conversion/decomposition proceeds bymeans of fermentation micro-organisms, whereby the nitrous content isreduced and the carbon dioxide is enriched.

[0044] In this process, solid and/or liquid residues 5 and gaseouswastes containing carbon dioxide are formed. The aerobic fermentation ispreferably executed in such a manner as to keep the organic mattermoving throughout in order to improve the gains and accelerate theprocess. To avoid the destruction of micro-organism communities, it ispreferable to take care that the organic matter is kept moving withoutmechanical aids.

[0045] A biochemical separation of the organic matter occurs duringaerobic fermentation, that offers the micro-organisms in the aerobicmethanogenesis stage a better chance of progressive functionality.Furthermore, biomass can be introduced by this process for the purposeof multiple utilisation. For instance, acetylsalicylic acid can in thisway be gleaned from grazing culture biomass. Another example is thederivation of pectin from brewery wastes. Yet another example is thatwhereby hecogenin acetate can be extracted form wastes from sisal fibremanufacture (jute production). By the method invented, the remainingresidual substance continues through the process of biogas production.

[0046] Another advantageous feature is that it can be preconfigured thatthe organic matter in the aerobic fermentation reactor 4 is churned upby means of an air supply or pneumatic through-flow system. In thismanner, the oxygen is supplied that is required for aerobic fermentationwhile the organic matter is churned up without mechanical stirringdevices.

[0047] In the next stage of the method invented, the solid and/or liquidresidues 5 are fed into a carbonisation plant 7 subsequent to anoptional dehydration. Such a carbonisation plant 7 is preferably a woodgasifier, which preferably functions by the cyclonic layering method. Byvirtue of another beneficial feature, it may be arranged that thegaseous waste containing carbon dioxide 6 is also fed into thecarbonisation process 7, specifically into the carbonising phase, inorder to facilitate the carbonisation process or to increase methanedelivery.

[0048] The carbonising facility 7 produces charcoal 8 as a final productand wood gas 9 that requires further processing and contains highproportions of carbon monoxide and carbon dioxide,—after passing throughan optional gas purification process 10—is fed into the third stage ofthe technique invented, a methanogenesis fermentation reactor 11. Thewood gas 6 from the carbonising facility 7 is hot and is preferably fedhot into the methanogenesis fermentation reactor 11. A preferredconfiguration of a methanogenesis fermentations reactor 11 is a tubereactor.

[0049] In the methanogenesis fermentation reactor 11, the wood gas 9 isfermented to biogas 12 with a high methane content by means ofthermophile methane fermentation under anaerobic conditions. Tosimultaneously counteract the destruction of micro-organism communities,it considered an additional beneficial feature that the organic matterin the thermophile methane fermentation is not kept moving by (e.g.) amechanical device.

[0050]FIG. 1 also illustrates how it can be considered an additionalbeneficial feature that further organic materials 13, especially thosecontaining lignin, can be carbonised in the carbonising reactor 7 alongwith residues 5 from the aerobic fermentation reactor 4.

[0051] Illustrated furthermore is how it can be regarded to be yetanother added beneficial feature that the methanogenesis fermentationreactor 11 may also be fed residues 5 (alternatively after dehydration)from the aerobic fermentation 4, together with wood gas 9 from thecarbonisation for conversion to methane.

[0052] A particularly beneficial, optional feature results from the factthat also otherwise sourced gases 14 containing carbon monoxide orcarbon dioxide can be fermented to methane together with wood gas 9 fromthe carbonisation 7.

1. Method for the production from organic matter (1) of biogas (12)containing methane, in which the organic matter (1) is decomposed andconverted to methane by means of living micro-organisms, characterisedthereby that, in an initial methodological step of the aerobicfermentation (4), organic matter (1) is fermented under aerobicconditions by means of fermentation micro-organisms, whereby solidand/or liquid residues (5) and gaseous wastes (6) containing carbondioxide are formed, in a second step of the method of carbonisation (7),residues (5) from the initial step of the method are carbonised, wherebya charcoal product (8) and wood gas (9) are formed, and in a third stepof the method of thermophile methane fermentation (11), wood gas (9)from the second step of the method is fermented under anaerobicconditions to biogas containing methane (12) by means of thermophilefermentation micro-organisms.
 2. Method according to claim 1,characterised thereby that the organic matter (1) is kept in motionduring the anaerobic fermentation (4).
 3. Method according to claim 2,characterised thereby that the organic matter is kept in motion withoutmechanical devices in aid.
 4. Method according to claim 2 or 3,characterised thereby that the organic matter (1) is kept in motion bymeans of an air supply or air infusion system.
 5. Method according toone of the claims heretofore, characterised thereby that also furtherorganic materials (13), especially materials containing lignin, arecarbonised together with residues (5) from the aerobic fermentation. 6.Method according to one of the claims heretofore, characterised therebythat gaseous waste (6) containing CO2 is introduced into carbonisation(7) from the aerobic fermentation (4).
 7. Method according to one of theclaims heretofore, characterised thereby that also residues (5) from theaerobic fermentation (4), together with wood gas (9) from thecarbonisation (7) are converted in the thermophile methane fermentation(11).
 8. Method according to one of the claims heretofore, characterisedthereby that also other gases (14) containing CO or CO² are fermented tomethane together with wood gas (9) from the carbonisation (7) in thethermophile methane fermentation (11).
 9. Method according to one of theclaims heretofore, characterised thereby that the organic matter (1) isnot kept in motion in the thermophile fermentation (11).
 10. Methodaccording to one of the claims heretofore, characterised thereby thatthe thermophile methane fermentation (11) is executed by means ofthermophile fermentation micro-organisms, whose optimal livingconditions lie in the range between 18° C. and 90° C., but preferablybetween 35° C. and 85° C., and especially between 45° C. and 55° C. or65° C.
 11. Method according to one of the claims heretofore,characterised thereby that the process is managed such that biogas (12)is produced with a methane content of at least 80%, but preferably atleast 85%, and especially preferred to reach at least 90%.
 12. Methodaccording to one of the claims heretofore, characterised thereby thatthe process is managed such that biogas (12) is produced with an H₂Scontent of less than 2%, but preferably less than 1% and especiallypreferred at less than 0.5%, 0.1% or 0.05%.
 13. Method for theproduction of methane rich biogas (12) from organic matter (1) by thedecomposition and conversion of organic matter (1) by means of livingmicro-organisms, particularly for the execution of a method according toone of claims 1 to 12, encompassing an aerobic fermentation reactor (4)for the fermentation of organic matter (1) under aerobic conditions bymeans of fermentation micro-organisms, whereby solid and/or liquidresidues (5) and gaseous wastes (6) containing CO² are formed, acarbonising facility (7) for the carbonisation of residues (5) from theaerobic fermentation reactor (4), whereby a charcoal product (8) andwood gas (9) are formed, and a methanogenesis fermentation reactor (11)for the execution of a thermophile methane fermentation, whereby woodgas (9) from the carbonising facility (7) is fermented by means ofthermophile fermentation micro-organisms under anaerobic conditions tobiogas containing methane (12).
 14. Mechanism according to claim 13,characterised thereby that the aerobic fermentation reactor (4) isequipped so as to keep the organic matter (1) in motion.
 15. Mechanismaccording to claim 14, characterised thereby that the aerobicfermentation reactor (4) is not equipped with any mechanical device inaid of keeping the organic matter (1) in motion.
 16. Mechanism accordingto claim 14 or 15, characterised thereby that the aerobic fermentationreactor (4) is equipped with an air supply or pneumatic through-flowsystem for keeping the organic matter in motion.
 17. Mechanism accordingto claim 13, characterised thereby that the methanogenesis fermentationreactor (11) is not equipped to maintain the organic matter (1) inmotion.